Parens right/left fragments are non-local and thus context dependent, more like sentence and paragraph structure than letter and word structure.
Parens arithmetic explicitly separates the operations of arithmetic from the standardization of how a number is written or displayed.
is a textual representation of containers that uses parentheses as delimiting tokens to stand in place of surrounding containers. page 
A parens form can be extruded upward and capped to construct stacks of boxes similar to parens trees, but with contact replacing connectivity.
Bounded forms are essentially identical to parens forms, but without the habitual linearity of typography.